The present invention relates to an infinitely variable cone-pulley belt-type transmission of the type having a drive-input shaft connected with the drive motor and a drive-output shaft, a respective pair of cone-pulleys arranged on each shaft, with one pulley of each pair being axially displaceable, and at least one endless transmission element running between two pulley pairs to transmit power therebetween. One axially displaceable cone-pulley of each pair cooperates with a piston fast with the associated shaft to form a cylinder-piston unit to which pressure medium supplied by a pump is distributed by way of a four-edged distributing slide valve for the setting and maintenance of the transmission ratio. The slide valve, on the one hand, acts on an axially movable cone-pulley and, on the other hand, is displaceable by the action of a control member. A biassed pressure relief control valve is connected in the path of outflow from the distributing valve for setting the pressure prevailing at the drive-output side of the transmission.
Such a transmission is disclosed in U.S. Pat. No. 3,451,283. There the biassed control valve is controlled by the pressure-medium pressure prevailing on the drive-input side of the transmission, so that in relation to a specific transmission ratio a torque-dependent control of the pressure-medium pressure on the drive-output side results.
If at this determined transmission ratio the torque to be conducted by the transmission should vary, this leads by way of the four-edged distributing slide valve finally to a corresponding modification of the pressure-medium pressure on the drive-input side, and thus by way of the control valve to a corresponding variation of the pressure-medium pressure on the drive-output side.
Now, however, this torque-dependent control system is affected by considerable inertia, since the adaptation to a modified torque can only take place by an adjusting operation initially involved therewith on one of the axially displaceable cone pulleys and takes effect upon the distributing slide valve. This leads to a resetting operation on the axially displaceable cone-pulley on the drive-input side, as a result of variation of the pressure-medium pressure prevailing there, only after which an adaptation of the pressure-medium pressure prevailing on the drive-output side can take place by the action of the modified pressure-medium pressure at the drive-input side upon the control valve. This behavior is especially disadvantageous in the case of torque surges such as occur especially in starting up, in gear change operations, etc.